Angular displacement sensor of compliant material

ABSTRACT

Disclosed is an apparatus including a compliant capacitor and an elongated structure extending between a first end and a second end. The elongated structure is compliant material that is flexible and bendable from a linear, non-bent position to multiple bendable positions and is an elastomer based material. The compliant capacitor includes a first conductive filler embedded within and extending from the first end to the second end along a longitudinal length of the elongated structure to form a first electrode of the compliant capacitor. The compliant capacitor also includes a second conductive filler embedded within and extending from the first end to the second end along the longitudinal length to form a second electrode of the compliant capacitor. The compliant capacitor further includes an elastomer dielectric layer extending between the first conductive filler and the second conductive filler.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/511,073filed Oct. 9, 2014, which is a continuation of U.S. application Ser. No.14/460,726 filed Aug. 15, 2014, now U.S. Pat. No. 8,941,392 issued Jan.27, 2015, which claims the benefit of U.S. Provisional Application No.61/867,047, filed Aug. 17, 2013, and U.S. Provisional Application No.62/003,030, filed May 27, 2014, the entire contents of all areincorporated herein by reference.

BACKGROUND

Sensors for measuring the strain of an object are ubiquitous in thefield of engineering. One type of known sensor is a capacitive strainsensor consisting of a non-conducting, compliant dielectric layersandwiched between two compliant conducting layers (also referred toherein as “compliant electrodes”). This arrangement forms a capacitorwhose capacitance depends in part on the distance between the conductivelayers and the change in surface area of the compliant conductinglayers. The strain and/or compression of the dielectric layer changesthe capacitance of the sensor, which can be detected by a sensingsystem. When a beam element is bent, a tensile strain is induced on theoutside of the curved beam element and a compressive strain is inducedon the inside of the curved beam element. If one or more compliantcapacitive strain sensors are embedded within the beam element such thatthey are displaced from the center axis of the beam element, the straininduced by bending results in a change in capacitance that can bedetected along the length of the beam element. This change incapacitance is proportional to the curvature of the bent beam element.In turn, this curvature is proportional to the angular displacementbetween two vectors defined by the ends of the beam element.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1A is a side view of a schematic portion of a sensor system,according to an embodiment of the present disclosure.

FIG. 1B is a cross-sectional view taken along section line 1B of FIG.1A, depicting components of an angular displacement sensor of the sensorsystem, according to another embodiment of the present disclosure.

FIG. 1C is a cross-sectional view taken along section line 1C of FIG.1A, depicting a spring electrode of the sensor system, according toanother embodiment of the present disclosure.

FIG. 2A is a side view of a sensor system, depicting an angulardisplacement of the angular displacement sensor, according to oneembodiment of the present disclosure.

FIG. 2B is a cross-sectional view of the angular displacement sensortaken along section line 2B of FIG. 2A, depicting a plane extendingalong an axis of the angular displacement sensor and orthogonal to awidth of compliant capacitors of the angular displacement sensor,according to another embodiment of the present disclosure.

FIG. 3 is a side view of the sensor system, depicting rigid ends of theangular displacement sensor extending substantially parallel relative toeach other, according to another embodiment of the present disclosure.

FIG. 4 is a side view of the sensor system, depicting the flexibility ofthe angular displacement sensor, according to another embodiment of thepresent disclosure.

FIG. 5A is a side view of the sensor system coupled over an anatomicaljoint of a leg, depicting rigid ends of the sensor system havingregistration members for attaching to the leg, according to anotherembodiment of the present disclosure.

FIG. 5B is a side view of the sensor system, coupled over an anatomicaljoint of an arm, according to another embodiment of the presentdisclosure.

FIG. 6 is a side view of the sensor system, depicting another embodimentof the registration members extending from the rigid members of theangular displacement sensor, according to the present disclosure.

FIG. 7 is a schematic of the sensor system, according to anotherembodiment of the present disclosure.

FIGS. 8A, 8B, and 8C are graph charts, depicting examples of calculateddata shown as angle verses time graphs, according to another embodimentof the present disclosure.

FIG. 9A is a perspective view of a sensor system, depicting the sensorsystem sensing angular displacement in a first plane and a second plane,according to another embodiment of the present disclosure.

FIG. 9B is a cross-sectional view of the angular displacement sensortaken along section line 9B of FIG. 9A, depicting the angulardisplacement sensor including first and second sets of compliantcapacitors for sensing angular displacement in a first plane and asecond plane, according to another embodiment of the present disclosure.

FIG. 9C is a side view of a sensor system coupled over an ankle joint,according to another embodiment of the present disclosure.

FIG. 10A is a simplified partial perspective view of an angulardisplacement sensor, depicting the angular displacement sensor includinga set of helical or spiral compliant capacitors for sensing twisting ortorque movement of the angular displacement sensor, according to anotherembodiment of the present disclosure.

FIG. 10B is a side view of the sensor system coupled over a shoulderjoint, according to another embodiment of the present disclosure.

FIG. 10C is a side view of the sensor system coupled over a hip joint,according to another embodiment of the present disclosure.

FIG. 11 is another embodiment of a sensor system for sensing angulardisplacement between two vectors, according to another embodiment of thepresent disclosure.

FIG. 12 illustrates another embodiment of a sensor system that includestwo instrumented registration members that are coupled to an angulardisplacement sensor, in accordance with some embodiments.

FIG. 13 illustrates another embodiment of a sensor system that includesone or more instrumented registration members that may be used to detectmovement of a body part, in accordance with some embodiments.

FIG. 14 is a side view of the sensor system, coupled over an anatomicaljoint, according to another embodiment of the present disclosure.

FIG. 15 illustrates a motion sensing system with a removable angulardisplacement sensor, in accordance with some embodiments.

FIG. 16 illustrates a linked motion measurement system, in accordancewith some embodiments.

FIG. 17 illustrates a diagrammatic representation of a machine in theexample form of a computer system, in accordance with some embodiments.

DETAILED DESCRIPTION

Described herein are various embodiments of sensor systems for sensingposition and movement of a joint with one, two or three rotationaldegrees of freedom, where each rotational degree of freedom can bedescribed by an angular displacement occurring with a plane that isorthogonal to the planes which define the other two rotational degreesof freedom. Also, described herein are methods of operating thesesensors systems to sense position and movement of a joint with one, twoor three rotational degrees of freedom. Compliant capacitive strainsensors have been described which can sense strain. A number of theseconventional compliant capacitive strain sensors are limited in themagnitude of strain they can be subjected to without incurring temporaryor permanent damage. Temporary or permanent damage may cause asubstantial increase in the resistance of the compliant electrodes ofthe compliant capacitive strain sensor or even a complete loss ofconductivity of these conventional compliant electrodes. Even ifconductivity is maintained, the resistance of conventional compliantelectrodes may increase to the point that the time response of thecompliant capacitive strain sensor is damaged. There are conventionalcompliant capacitive strain sensors that can perform measurements ofbending movements, but these strain sensors have restraining elements tolimit bending to prevent damage resulting from over straining. Also,these strain sensors themselves are configured to measure bendingmovement in one plane only. As such, the structural properties of suchsensors may provide for limited bending and flexibility and, therefore,may be limited in their potential uses. The aforementioned conventionalcompliant capacitive strain sensors for sensing bending movements may belimited in their ability to measure bending in a single plane. Bendingin a second orthogonal plane and/or torsion in a third orthogonal plane,may further compound conventional compliant capacitive strain sensorsability to quantify joints with more than one degree of freedom.

Embodiments of the present disclosure address the deficiencies describedabove and possibly other deficiencies of conventional sensor systems byproviding an angular displacement sensor that can measure unrestrictedbending movement on one or more orthogonal planes and withoutrestraining members which restrict flexibility. The angular displacementsensor may be a flexible elongated structure or a general bendingstructure that has embedded strain sensing elements that could take anyform. The angular displacement sensor as described herein may include acompliant strain sensing element, such as a compliant capacitor, withinan elongated structure of compliant material. The elongated structureextends between a first end and a second end. The compliant material isflexible and bendable from a linear, non-bent position to multiplebendable positions. The compliant capacitor, for example, includes 1) afirst conductive layer embedded within the compliant material andextending from the first end to the second end along a longitudinallength of the elongated structure to form a first electrode of the firstcompliant capacitor within the compliant material, 2) a secondconductive layer embedded within the compliant material and extendingfrom the first end to the second end along the longitudinal length toform a second electrode of the first compliant capacitor within thecompliant material, and 3) an elastomer dielectric layer extendingbetween the first conductive layer and the second conductive layer.Alternatively, the compliant strain sensing element may be resistive innature, capacitive in nature, or inductive in nature. Regardless of thenature of the compliant strain sensing element, an electrical propertyof the compliant strain sensing element changes in proportion to anapplied strain on the elongated structure as described herein in detail.

Referring to FIG. 1A, a sensor system 10 for sensing angulardisplacement between two vectors defined by rigid members is provided.The sensor system 10 may include an angular displacement sensor 12 witha highly bendable and flexible elongated structure 14. The angulardisplacement sensor 12 may be disposed within the structure 14 along afirst axis extending between a first end and a second end of thestructure 14.

In some embodiments, the sensor system 10 may include an angulardisplacement sensor 12 with a highly bendable and flexible elongatedstructure 14 having a first rigid member 16 and a second rigid member 18fixed to opposing ends of the angular displacement sensor 12. The sensorsystem 10 may also include an interface device 20 that may be coupled toone of the rigid members. The interface device 20 may be secured to auser or object (not shown) and include various electronic components,such as a micro-controller and memory, for receiving data relative to anangular displacement, discussed in further detail herein. Further, theinterface device 20 may be operatively coupled to a remote device 22 fora user to view and analyze the data received from the interface device20.

As set forth, the angular displacement sensor 12 may be an elongatedstructure 14 that defines an axis 24 along a longitudinal length 26thereof and extends between a first end 28 and a second end 30 of theangular displacement sensor 12. The first end 28 of the elongatedstructure 14 may be coupled to the first rigid member 16. Likewise, thesecond end 30 of the elongated structure 14 may be coupled to the secondrigid member 18. In one embodiment, the angular displacement sensor 12may transmit signals generated from the strain induced by bending alongthe elongated structure 14 utilizing one or more compliant capacitorsextending along the length of the angular displacement sensor 12.

In one embodiment, the sensor system 10 may include a first compliantstrain sensing element embedded within a compliant material andextending from the first end 28 to the second end 30 along alongitudinal length of the elongated structure 14. The first compliantstrain sensing element may include a second compliant material that isflexible and bendable. In some embodiments, an electrical property ofthe first compliant strain sensing element changes in proportion to anapplied strain on the elongated structure 14. The first compliant strainsensing element may be resistive in nature, where resistance of thesecond compliant material changes in proportion to the applied strain onthe elongated structure 14. The first compliant strain sensing elementmay be inductive in nature, where an inductance of the first compliantstrain sensing element changes in proportion to an applied strain.

In another embodiment, the angular displacement sensor 12 may utilizesimilar principles employing compliant inductive or resistive strainsensing elements. Further, for example, the angular displacement sensor12 may be made of an elastomer based material with various electrodelayers, dielectric layers, and other components set forth herein thatenable the angular displacement sensor 12 to hold the structuralcharacteristics of being highly flexible and bendable without breakingthe electrical circuit along the length 26 of the angular displacementsensor 12.

With reference to FIGS. 1A (a side view) and 1B (an axial view of across section of angular displacement sensor 12), the various layers andcomponents of the angular displacement sensor 12 will now be described,according to one embodiment. The angular displacement sensor 12 mayinclude three primary portions: a first compliant capacitor 32 and asecond compliant capacitor 34 with a base elastomer layer 36 extendingtherebetween, each of which extend along the longitudinal length 26 ofthe angular displacement sensor 12 in layers or portions. In someembodiments, the angular displacement sensor 12 includes one compliantcapacitor, which may be either the first compliant capacitor 32 or thesecond compliant capacitor 34. Each of the first and second compliantcapacitors 32, 34 includes an outer electrode 38 and an inner electrode40 with an elastomer dielectric 42 therebetween. Each of such outer andinner electrodes 38, 40 with the elastomer dielectric 42 therebetweenalso extend as a layer along the longitudinal length 26 that each definea similar width 44, the width 44 defined as being transverse to thelength 26 and within the same plane as the dimension of the length 26 ofthe elongated structure 14. The outer and inner electrodes 38, 40 mayalso define a thickness or depth (the dimension extending orthogonalrelative to the width 44 and length 26 dimensions) such that the outerand inner electrodes 38, 40 of each of the first and second compliantcapacitors 32, 34 may include a similar thickness or depth in the rangeof about 10-500 microns. The elastomer dielectric 42 disposed betweenthe outer and inner electrodes 38, 40 may define a thickness or depth ofabout 10 to 200 microns. In addition, the base elastomer layer 36positioned between the first and second compliant capacitors 32, 34 mayinclude a depth in the range of about 0.5-5 mm. Such primary layers ofthe angular displacement sensor 12 may also include an outer layer 46 orportion (or coating) that may include a thickness of about 0.5-3 mm thatis non-conductive and an elastomeric based material.

The base elastomer layer 36 or middle portion of the angulardisplacement sensor 12 may be either a thermoset or thermoplasticelastomer. Further, the base elastomer layer 36 is a dielectric materialand non-conductive. The base elastomer layer 36 may include structuralcharacteristics of high elongation at failure greater than 100% andpreferably greater than 500%, a low durometer preferably at a 60 Shore Ascale, but may be anywhere in the range of 1-90 on the Shore A scale. Inaddition, the base elastomer layer 36 may include a low compression setof 1-30%. In one embodiment, a thermoset elastomer may include tin orplatinum cured silicone elastomers and/or polyurethane elastomercomponents or any other suitable elastomer material. In anotherembodiment, a thermoplastic elastomer may include components ofstyrene-ethylene/butylene-styrene (SEBS),styrene-block-butadiene-block-styrene (SBS), and/or polyurethanes or anyother suitable thermoplastic elastomer.

The first and second compliant capacitors 32, 34 of the angulardisplacement sensor 12 may be a partially conductive material (and anelastomer based material) so as to store a charge and be formed overopposite sides of the base elastomer 36. As previously set forth, eachof the first and second compliant capacitors 32, 34 may include theouter and inner electrodes 38, 40 with the elastomer dielectric 42therebetween. The elastomer dielectric 42 between the outer and innerelectrodes 38, 40 may be non-conductive and formed of a similar materialas the base elastomer 36. The outer and inner electrodes 38, 40 may beformed along a length 26 of the elongated structure 14 as layers of anelastomer based material with a conductive filler. In one embodiment,the conductive filler may include powdered or flake metals, such assilver flake, carbon black and fibrous materials such as carbonnanofibers, carbon nanotubes, silver nanostrands or any other suitableconductive filler particles. It is preferable to use the minimum amountof conductive filler particles as possible, as excess fillerconcentrations alters the elastic behavior of the elastomer. Excessiveconductive filler particles may limit the ability of the angulardisplacement sensor 12 to effectively bend and result in an electricalcircuit break through bending the angular displacement sensor 12. Theembodiments described herein may facilitate maximum bending by limitingthe conductive filler particles in the elongated structure 14. As such,to minimize the conductive filler in the electrode layers to, thereby,minimize breaking the electrical circuit in the outer and innerelectrodes 38, 40, the elongated structure 14 may also include aconductive wire member.

Now with reference to FIGS. 1B and 1C, the conductive wire member mayextend continuously through the elongated structure 14 between the firstand second ends 28, 30 thereof. In one embodiment, the wire member mayinclude a wave configuration, similar to a sine wave, and be aspring-like structure, referenced as a spring electrode 50. The springelectrode 50 may be made from a conductive metal and may be formed in ashape that can easily elongate, compress, and twist about or along theaxis 24 of the angular displacement sensor 12. The spring electrode 50may be formed from a wire or laser cut from flat sheets, or formed viaetching photolithography techniques. The material of the springelectrode 50 may be any conductor, including stainless steel, copper,super-elastic materials, such as Nitinol, or any other suitableconductive material. In one embodiment, the spring electrode 50 mayextend in a flat configuration or be planer with the wave configuration,as depicted. In another embodiment, the spring electrode 50 may behelical or some other three-dimensional shape such that the helicalconfiguration extends through the conductive layers. In anotherembodiment, the conductive layers may extend through the elongatedstructure 14 in a helical configuration with the spring electrode 50disposed along the conductive layers.

The spring electrode 50 may be embedded through each of the layers ofthe outer and inner electrodes 38, 40. In another embodiment, the springelectrode 50 may be positioned over a surface of each of the outer andinner electrodes 38, 40. Each of the outer and inner electrodes 38, 40may include its own spring electrode 50, separate and discrete from eachother. The spring electrodes 50 are intended to make electrical contactwithin the compliant electrode layers, and as such, may be just touchingthe electrode material or either partially or fully embedded in thecompliant electrode layers. Further, the spring electrode 50 may bepositioned over or in each of the outer and inner electrodes 38, 40 bylaying the spring electrode 50 onto the surface of the outer and innerelectrodes 38, 40 and pressing the spring electrode 50 into the surface,which may embed at least a portion of the spring electrode 50 into theelectrode layers. With the spring electrode 50 at least partiallyembedded into each of the outer and inner electrodes 38. 40, such springelectrode 50 minimizes potential breaks in the electrical circuit in theconductive elastomer of the outer and inner electrodes 38, 40. Suchspring electrode 50 may maintain a proper electrical circuit andconnection to minimize potential circuit breaks in instances, forexample, where the angular displacement sensor 12 is moved to a maximumbent position, the angular displacement sensor 12 becomes fatiguedthrough reiterative minimal or maximum bending, and/or unforeseeninstances where the angular displacement sensor is misused ormishandled. Further, the spring electrode 50 places little to noresistance to the bendability of the angular displacement sensor 12.Furthermore, the spring electrode 50 facilitates minimizing theconductive filler particles of the outer and inner electrodes, thus,maximizing the bendability of the angular displacement sensor 12. Inthis embodiment, as previously set forth, there may be two pairs ofouter and inner electrodes 38, 40 and, thus, there would be four springelectrodes 50 extending through the angular displacement sensor 12, onefor each electrode layer. Of course, there may be instances where theremay be more spring electrodes or conductive wire members per electrodeor additional electrodes each containing at least one conductive wiremember. In addition, the spring electrodes 50 facilitate coupling theouter and inner electrodes 38, 40 to wire leads (not shown) extending inone or both of the first and second rigid members 16, 18 fortransferring measurement data from the first and second compliantcapacitors 32, 34. Such wire leads transfer measurement data to adifferential capacitance measurement circuit 112 (FIG. 7), discussed infurther detail herein.

With respect to FIGS. 1A and 2A, the sensor system 10 is depicted in alinear non-bended, first position and a bended, second position,respectively. As previously set forth, the sensor system 10 may includethe angular displacement sensor 12 or middle region that is an elastomerbased material formed into an elongated structure 14 that is highlyflexible and/or bendable. The sensor system 10 may include an elongatedstructure 14 extending between a first end 28 and a second end 30. Theelongated structure may be a compliant material that is flexible andbendable from a linear, non-bent position to multiple bendablepositions. The first and second ends 28, 30 of the angular displacementsensor 12 are embedded within or attached to the respective first andsecond rigid members 16, 18 that may also be somewhat elongated andpreferably symmetrically formed around the first and second ends 28, 30of the angular displacement sensor 12. The rigid members 16, 18 mayfully or partially embed the angular displacement sensor ends 28, 30.Alternatively, the rigid members 16, 18 may be embedded within theangular displacement sensor ends 28, 30 either partially or fully.Furthermore, the rigid members 16, 18 may take the form of adhesives,screws, welds, or other form of attachments between the sensor ends 28,30 and the substrate to which the angular displacement sensor 12 isattached. The substrate to which the angular displacement sensor 12 isattached may include plastic, metal, ceramics, fabric, elastomers andthe like. The first and second rigid members 16, 18 may define a firstvector 52 and a second vector 54, respectively. In the linear non-bendedposition, the first and second vectors 52, 54 may be substantiallyco-axial with the axis 24 of the elongated structure 14 or co-axial withthe angular displacement sensor portion itself.

In the non-linear bended position, the first and second rigid members16, 18 may become displaced such that the elongated structure 14 isnon-linear or moved to a bent position. In this bent position, the firstand second vectors 52, 54 defined by the respective first and secondrigid members 16, 18 define an angle or, otherwise referenced herein as,an angular displacement 60 between the first and second rigid members16, 18. In one embodiment, the angular displacement 60 may be determinedfrom, for example, a horizontal line 56, relative or parallel to theaxis 24 of the angular displacement sensor 12 in the linear position,taken from an intersection 58 of the first and second vectors 52, 54. Assuch, the angular displacement 60 may be equal to a first vector angle62 minus a second vector angle 64, in which the first vector angle 62may be defined between the horizontal line 56 and the first vector 52and the second vector angle 64 may be defined between the horizontalline 56 and the second vector 54. Other angles, such as an acute angle66 defined between the second vector 54 and the horizontal line 56, mayalso be of interest and may have need to be analyzed, which may readilybe calculated as a parameter, as known to one of ordinary skill in theart. In this manner, the sensor system 10 may provide measurement datato calculate the angular displacement 60 between the first and secondvectors 52, 54 defined by the first and second rigid members 16, 18. Theangular displacement sensor 12 also may provide measurement data as tothe change in the angular displacement 60 over time as well a rate ofchange of the angular displacement 60 between the first and secondvectors 52, 54 defined by the first and second rigid members 16, 18.

The angular displacement 60 is measured, as well as each of the abovenoted angles, with a differential measurement based on the capacitanceoutput of the first and second compliant capacitors along the length 26of the elongated structure 14 or angular displacement sensor 12. Theangular displacement 60 is detected by measuring the capacitance betweenthe inner and outer electrodes of each of the first and second compliantcapacitors 32, 34. The differential measurement of the first and secondcompliant capacitors increases the sensitivity and reduces common modenoise. In some embodiments, the first and second compliant capacitors32, 34 are spaced in a parallel manner such that a sensitivity of theangular displacement is increased. The first and second compliantcapacitors are offset from a center axis of the elongated structure andare reflected about the center axis. In some embodiments where theangular displacement sensor 12 includes a single compliant capacitor,the angular displacement 60 is detected by measuring the capacitancebetween the inner and outer electrodes of the single compliantcapacitor.

Upon the first and second rigid members 16, 18 being in a co-axialposition, as shown in FIG. 1A, the measurement data transmitted from theangular displacement sensor 12 will indicate substantially no angulardisplacement. The same is true upon the first and second rigid members16, 18 being parallel with each other since any positive/negativecapacitance generated due to bending in the angular displacement sensor12 will cancel each other out. On the other hand, upon the rigid membersbeing moved to an orientation that is non-coaxial or non-parallel, suchas that shown in FIG. 2A, the capacitance measurements provided by theangular displacement sensor 12 may provide an angular displacement 60relative to the orientation between the first and second vectors 52, 54defined respectively by the first and second rigid members 16, 18.

With respect to FIGS. 2A and 2B, in one embodiment, the angulardisplacement 60 is calculated along and within a first plane 70 or aprojection or component of the first plane 70 relative to the first andsecond rigid members 16, 18 and the angular displacement sensor 12. Inother words, due to the flexibility of the elongated structure 14, thefirst and second rigid members 16, 18 and/or elongated structure 14 mayextend out of the first plane 70 and, thus, the angular displacement 60that may be measured may be a projection or components of the firstplane 70 relative to the actual position of the angular displacementsensor 12. The first plane 70 may be defined as a plane correspondingwith and/or extending along the axis 24 of the angular displacementsensor 12 and extending substantially orthogonal to the width 44 of thefirst and second compliant capacitors 32, 34 of the angular displacementsensor 12. The width 44 of the compliant strain sensor 44 may be definedas the dimension orthogonal to the longitudinal length 26 (see FIGS. 1Aand 1B), the width 44 and length 26 dimensions extending within the sameplane. In some embodiments, the width of the compliant strain sensor 44may be defined as a distance between the two sides of the compliantstrain sensor 44 that lie within a plane perpendicular to an axis of theelongated structure and perpendicular to the plane in which angulardisplacement is being measured such that this axis corresponds to theangular displacement sensor 12.

Furthermore, the angular displacement 60 may be defined solely by theangle between the first and second vectors 52, 54 defined by the firstand second rigid members 16, 18. That is, the sensor system 10 may onlyprovide measurement data for the angular displacement 60 relative to thefirst and second vectors 52, 54 and is insensitive to the path of theangular displacement sensor 12, including any wrinkles, kinks, out ofplane bending, etc. of the angular displacement sensor 12 itself. Forexample, in FIG. 2A, the angular displacement sensor 12 is bent similarto an “M” configuration. However, as set forth, the differentialmeasurement of the first and second compliant capacitors (FIG. 2B) islimited to the angular displacement 60 of the first and second vectors52, 54 defined by the first and second rigid members 16, 18.

Further, for example, FIG. 3 depicts the angular displacement sensor 12of the sensor system 10 being bent in several locations similar to an“S” configuration. However, in this “S” configuration, the first andsecond vectors 52, 54 defined by the respective first and second rigidmembers 16, 18 are substantially parallel to each other and, thus, thereis no angular displacement between the first and second vectors 52, 54.In this manner, the positive and negative capacitance measurements ofthe angular displacement sensor 12 in the differential measurement wouldcancel each other out to provide measurement data with no angulardisplacement between the first and second vectors 52, 54.

In another example, FIG. 4 depicts the high flexibility of the angulardisplacement sensor 12 such that the angular displacement sensor 12 maybend over itself as it is a highly bendable elastomer based sensor(without restraint), as previously set forth. The non-restrainedflexible angular displacement sensor 12 of the present embodiment isadvantageous as such an angular displacement sensor 12 may be employedover a variety of anatomical joints or for other useful purposes withlimited potential of breaking its electrical circuit therein. It isnoted that a non-restrained flexible angular displacement sensor 12 maybe defined as not having one or more members associated with the angulardisplacement sensor 12 to positively limit its flexibility orbendability, but rather, the non-restrained flexible angulardisplacement sensor 12 may only be restrained by the elastomer basedmaterials of the angular displacement sensor 12 itself. As such, thenon-restrained angular displacement sensor 12 may be employed withoutbreaking the electrical circuit along the first and second compliantcapacitors in the angular displacement sensor 12 due to the springelectrodes 50 (FIGS. 1B and 1C) positioned within each of the outer andinner electrodes 38, 40 of the compliant capacitors 32, 34, as describedherein, or by utilizing a conductive elastomeric electrode material(such as an elastomer with certain fibrous conductive filler materials,such as carbon nanotubes) that maintains conductivity at high strains.Further, as depicted in FIG. 4, the sensor system 10 calculates theangular displacement 60 between the first and second vectors 52, 54defined by the respective first and second rigid members 16, 18,regardless and accounting for the minimized radius or bend in theangular displacement sensor 12.

Now with reference to FIG. 5A, the sensor system 10 is depicted in usewith the angular displacement sensor 12 extending over an anatomicaljoint 80, such as a knee joint, with the first and second rigid members16, 18 coupled to a leg 82 of a person or user 84. In one embodiment,the first and second rigid members 16, 18 may each include aregistration member 90 coupled, secured, or attached thereto. Theregistration member 90 may include one or more straps 92 to form a straparrangement. Such straps 92 may be adhesively attached or sewn to thefirst and second rigid members 16, 18 and may include one or more straps92, including hook and loop fasteners such as in the Velcro® straps, toreadily attach and remove the one or more straps 92 from one's leg 82,for example. In this manner, the registration member 90 may wrap around,for example, a person's leg 82 under or over clothing to fixedly orientand position the first and second rigid members 16, 18 proximal anddistal the anatomical joint 80 of the user 84.

In another embodiment, the registration member 90 associated with thesensor system 10 and angular displacement sensor 12 may include flangeportions 94 in a fin-like structure, as depicted in FIG. 6.Alternatively, the flange portions 94 may be in a rectangular,ellipsoidal or other geometrically shaped structure. In this embodiment,the first and second rigid members 16, 18 may be disposed in a pocket,slot or sleeve of one's clothing (not shown) that is sized andconfigured to receive the flange portions 94 of the registration member90 such that the registration member is integrated with the clothingitself. Of course, the flange portions 94 may include otherconfigurations that include a surface area that will maintain the rigidmembers in a fixed orientation adjacent the anatomy that may beintegrated into clothing. In another embodiment, the first and secondrigid members 16, 18 may simply be integrated within clothing, withoutflange portions, in a manner that will hold the first and second rigidmembers 16, 18 in a substantially fixed orientation within the clothing.In this manner, the registration member 90 may be sized and configuredwith any suitable structure for being fixedly positioned to the anatomyof the person or user. With respect to FIGS. 5A and 6, in anotherembodiment, the registration member 90 may replace the first and secondrigid members 16, 18 such that the registration member 90 facilitatespositioning the first and second ends 28, 30 (FIG. 1A) of the angulardisplacement sensor 12 in a substantially fixed position against theanatomy of the user 84 to act or perform as a rigid member.

Referring back to FIG. 5A, in one embodiment, the first rigid member 16may be positioned proximal and above the anatomical joint 80 and thesecond rigid member 18 may be positioned distal and below the anatomicaljoint 80. Such first and second rigid members 16, 18 may be positionedso that the angular displacement sensor 12 or middle portion of thesensor system 10 may extend over or adjacently along the side of theanatomical joint 80. The interface device 20 may be coupled to the waistof the user 84 or simply placed in the user's pocket or the like. As theuser 84, for example, performs a walking or running motion, the angulardisplacement sensor 12 bends along multiple bent positions between thefirst and second rigid ends 28, 30. Upon undergoing such motion, theinterface device 20 receives, logs and saves data relative to theangular displacement 60 between the first and second vectors 52, 54. Inthis manner, the logged data may then be transmitted to the remotedevice 22 wirelessly to, for example, a mobile device 100 (e.g., smartphone) using wireless technology or transferred with, for example, astorage device via a wired connection (e.g., universal serial bus (USB)port) to a personal computer 102. Other means for transferring loggeddata to the remote device 22 may be employed, as known to one ofordinary skill in the art having the benefit of this disclosure. Oncetransferred to the remote device 22, the logged data may be put invarious formats useable for analysis. In this example where the angulardisplacement sensor 12 is positioned over a knee joint, the user orphysician may better understand the person's gait, as well as the rateof angular displacement 60 and even the change in the angulardisplacement 60 of the person changing from a walking motion to arunning motion. In this manner, the logged data may be transferred tothe remote device 22, saved, and viewable for later analysis. Further, aphysician, for example, may chart the progress/decline and comparedifferences in the user's gait over various sessions and periods oftime.

The sensor system 10 may be employed for similar analysis to graph andanalyze other anatomical joints 80, such as an elbow joint, as depictedin FIG. 5B. The elbow joint is similar to the knee joint in that theelbow joint moves substantially within a single plane or a first plane70 (see FIG. 2B). As such, the first rigid member 16 may be positionedproximal the elbow joint and the second rigid member 18 may bepositioned distal the elbow joint with the angular displacement sensor12 extending over or adjacent the side of the elbow joint. The sensorsystem 10 may undergo reiterative arm movements at the elbow joint inwhich the sensor system 10 measures and calculates data relative to theangular displacement 60 between the first vector 52 and the secondvector 54 defined by the respective first and second rigid members 16,18. Similar to that described relative to FIG. 5A, the data may belogged and transferred to a remote device 22 for analysis. For example,a user 84 or patient may be injured and undergoing rehabilitativephysical therapy and precise measurements of the angular displacement 60may be useful to understanding the progress or decline of the patient 84over various sessions and periods of time.

With respect to FIG. 7, a schematic diagram or flow chart of variouscomponents of a system for analyzing data relative to angulardisplacement of the sensor system 10, according to one embodiment, isprovided. In this embodiment, the primary components may include thesensor system 10, the interface device 20, and the remote device 22. Thesensor system 10 may include the angular displacement sensor 12 and abiofeedback device 110. The interface device 20 may include acapacitance measurement circuit 112, a micro-controller 114, abiofeedback amplifier 116, and a user interface 118. Themicro-controller 114 may include a calculation circuit 120, a memory122, and control and analysis software 124. The remote device 22 mayinclude a display 126 and user input 128, and may include the processorsand computing devices of, for example, a smart phone or personalcomputer, as known in the art. In other embodiments, themicro-controller 114 may include both analog and digital circuitry toperform the functionality of the capacitance measurement circuit 112,the calculation circuit 120, and biofeedback amplifier 116.

In use, for example, upon bending movement of the angular displacementsensor 12, the capacitance measurement circuit 112 measures capacitancesof the compliant capacitors 32, 34 of the angular displacement sensor12. As illustrated in FIG. 7, the capacitance measurement circuit 112can be housed in the interface device 20 and coupled to the angulardisplacement sensor 12 via wires, as indicated by arrow 130Alternatively, the capacitance measurement circuit 112 may be housedadjacent to or with the angular displacement sensor 12 itself (asindicated with dashed arrow 130′ in FIG. 7) or within, for example, oneof the first and second rigid members (not shown) coupled to the angulardisplacement sensor 12. It should be noted that the capacitancemeasurement circuit 112 can measure a first capacitance between theinner electrode 40 and outer electrode 38 of one of the compliantcapacitors 32, 34. The capacitance measurement circuit 112 can alsomeasure a second capacitance between the inner electrode 40 and outerelectrode 38 of the other one of the compliant capacitors 32, 34. Inanother embodiment, the capacitance measurement circuit 112 can measurea differential capacitance of the two compliant capacitors 32, 34. Whenthe angular displacement sensor 12 includes the single compliantcapacitor, as described herein, the capacitance measurement circuit 112can measure a single capacitance between the inner and outer electrodesof the single compliant capacitor. The capacitance measurement circuit112 can measure the capacitance(s) or differential capacitance in termsof voltage. The capacitance measurement circuit 112 then transmitsvoltage data to the micro-controller 114, such as to the calculationcircuit 120, as indicated by arrow 132. The calculation circuit 120calculates the values of the voltage data provided by the capacitancemeasurement circuit 112 to calculate the angular displacement 60 (seeFIG. 5A) between the first and second vectors 52, 54 defined by thesensor system 10, as previously described. The calculation circuit 120may then transmit angle data to the memory 122 (which then becomeslogged data) and the control and analysis software 124, as indicated byrespective arrows 134, 136. In one embodiment, parameters may be inputas maximum/minimum limits for angular displacement through, for example,the user interface 118. The user interface 118 may include a displayand/or a user input, such as input keys. The maximum limits (and minimumlimits) may be useful for a user to know once the user has reached aparticular angular displacement with the sensor system 10. As such, ifthe user does meet the desired parameters (or undesired as the case maybe), the control and analysis software 124 may transmit a signal to thebiofeedback amplifier 116, as indicated by arrow 138, which in turn maytransmit a signal back to the biofeedback device 110, as indicated byarrow 140, at the sensor system 10.

The biofeedback device 110 may then produce a notification to the userthat a predefined input parameter has been reached, such as the maximumangular displacement, so that the user understands in real-time thelimits relative to the movement of the user's particular joint beinganalyzed. The notification may be at least one of a visual notification,an audible notification, and a tactile notification or some othernotification to facilitate the user's understanding of the user'smaximum limit. Alternatively, the notification can be any combination ofvisual, audible and tactile notifications. The visual notification maybe in the form of a blinking (or various colored) light or the likedisplayed on the sensor system 10 itself or the interface device 20and/or also may be visualized on a display of the interface device 20.The audible notification may be a ring or beep or the like that maypreferably be audibly transmitted from the interface device 20, but mayalso be transmitted from the sensor system 10. The tactile notificationmay be coupled to or integrated with one of the first and second rigidmembers 16, 18 (FIG. 5A) of the sensor system 10 or may be integrated inthe interface device 20. Such tactile notification may be in the form ofa vibration or some other tactile notification, such as a compressionmember. In this manner, the biofeedback device 110 may notify the userin real time upon extending or contracting ones anatomical joint at amaximum angular displacement according to a predetermined inputparameter. Similarly, in another embodiment, a user may input parametersof a minimum angular displacement into the interface device 20 forbiofeedback notification. Further, in another embodiment, the user mayinput parameters for both a minimum angular displacement and a maximumangular displacement. Inputting such parameters may be useful forexercises during physical therapy and for athletes training to obtainparticular movements at various anatomical joints.

Upon completing a session of rehabilitation therapy or training or thelike, logged data 142 may be stored in the memory 122 or storage deviceof the interface device 20. Such logged data 142 may also be viewable onthe interface device 20 on a display at the user interface 118. Thelogged data 142 may then be transferred to the remote device 22, asindicated by arrow 144. The remote device 22 may be any known computingdevice, such as a mobile device, smart phone, tablet, personal computer,gaming system, etc. In one embodiment, the logged data 142 may betransferred to a smart phone by, for example, wireless technology (e.g.,over a wireless local area network (WLAN) such as a Bluetooth® networkor Wi-Fi® network) or transferred via mini-USB ports or the like, asknown to one of ordinary skill in the art. In another embodiment, thelogged data 142 may be transferred to a personal computer via a port,such as a USB port with, for example, a portable memory device, such asa thumb drive. The user may then save the logged data 142 on the remotedevice 22 for further analysis. As previously set forth, the user maysave several sessions of logged data 142 to the remote device 22 toobtain further analysis and comparison data to better understand, forexample, progress or regress in the user's angular displacement of theuser's anatomical joints.

As depicted in FIGS. 8A, 8B, and 8C, one embodiment of logged data 142provided by the sensor system coupled to a user's knee joint, similar tothat depicted in FIG. 5A, is provided. For example, FIG. 8A graphslogged data 142 that a user may view on a remote device 22, such as, apersonal computer, in the form of a graph 150, providing logged data 142of the angular displacement 60 at the knee joint verses time of the userperforming a walking motion. As depicted, the logged data 142 providesthe user's gait with an angular displacement 60, depicting a maximumangle 152 of about 60 degrees with a minimal bump angle 154 of about15-20 degrees between each maximum angle 152. Further, between eachmaximum angle 152 and minimal bump angle 154, the user's leg extendsalmost vertical or at about a zero angular displacement 156. Such loggeddata 142 also provides detail relative to the rate of the user's walkingor gait.

In another example, FIG. 8B provides logged data 142 in graph format ofa user jogging, providing detail of the angular displacement versestime. The graph of the user jogging is similar to the user walking,except the maximum angle 152 ranges between 110 and 115 degrees with theminimal bump angle 154 of about 40 degrees. Further, the angulardisplacement 60 of the knee joint does not appear to ever register at azero angular displacement or extend linearly, but rather, alwaysmaintains a minimal angular displacement 158 of at least 20 degrees.FIG. 8C provides logged data 142 in graph format of a user performing asquatting motion, showing detail of the angular displacement 60 of theknee while squatting verses time. In this embodiment, the angulardisplacement 60 moves between a minimal angular displacement 156 ofabout zero degrees and the maximum angle 152 of about 120 degrees.

As described above, such logged data 142 may be useful for physicaltherapists for recording improvement in persons recovering from aninjury. Similarly, physicians may desire to record and analyze thedecline of a patient with an illness. Further, athletes may be able toutilize such logged data in order to analyze their gait and tounderstand where improvements can be made and compare past logged datato view and analyze such improvements. Furthermore, with respect toFIGS. 5A and 7, as previously discussed herein, the sensor system 10 mayinclude the biofeedback device 110. The biofeedback device 110 may beintegrated with one of the rigid ends or in the interface device 20. Thebiofeedback device 110 may be sized and configured to alert or notifythe user of a maximum or minimum angular displacement that the user 84inputs as a parameter in which the joint should or should not extend (orcontract or twist, see FIG. 10A). In one embodiment, the biofeedbackdevice 110 may exhibit a flashing light, provide a tactile signal (e.g.,vibration), and/or provide an audible sound, so that the user 84 isnotified of a predetermined angular displacement 60 or movement of one'sjoint.

For example, during rehabilitative physical therapy, the sensor system10 may be programmed with a parameter to activate the biofeedback device110 upon moving one's leg at the given predetermined angle translated asthe angular displacement 60 between the first and second vectors 52, 54defined by the relative first and second rigid members 16, 18. The user84 may attach the sensor system 10 to, for example, one's leg to extendalong the anatomical joint 80, such as the knee joint. The user 84 mayundergo physical therapy by reiterating certain movements of the kneejoint such that the predetermined angle is set so that the biofeedbackdevice 110 notifies the user once the correct movement or angle has beenobtained or met. Likewise, the sensor system 10 can be programmed tonotify the user 84 prior to exceeding an angular displacementcorresponding with the anatomical joint 80 that the user is making tominimize joint movement that may be harmful to the user. In this manner,the sensor system 10 can be utilized for physical therapy or the like.Also, as previously set forth, the sensor system 10 may be employed forother anatomical joints of the anatomy, such as the ankle joint, theshoulder joint, and/or the hip joint. As will be apparent to one ofordinary skill in the art, some joints in the body allow bendingmovement and/or rotational movement outside of a single plane. As such,the sensor system 10 may be sized and configured with additionalcompliant capacitors to account for bending of the sensor in additionalplanes or rotational movement.

For example, with respect to FIGS. 9A and 9B, another embodiment of asensor system 210 is provided. In this embodiment, the sensor system 210may include an angular displacement sensor 212 with an elongatedstructure 214 with first and second rigid members 216, 218 at opposingends of the elongated structure 214. The sensor system 210 of thisembodiment is similar to the embodiments described above, except in thisembodiment, the angular displacement sensor 212 may include anadditional pair of compliant capacitors, resulting in a total of fourcompliant capacitors 232, 234, 236, 238, described in more detail below.The angular displacement sensor 212 may also include a round periphery,as shown in the cross-sectional view of FIG. 9B, however such may alsoinclude a square, rectangular, ellipsoidal, or round periphery, or anyother regular or non-regular shape. The angular displacement sensor 212includes first and second compliant capacitors 232, 234 or a first setof compliant capacitors extending along the longitudinal length of theangular displacement sensor 212, similar to embodiments described above.In addition, the angular displacement sensor 212 includes third andfourth compliant capacitors 236, 238 or a second set of compliantcapacitors oriented orthogonally relative to the first and secondcompliant capacitors 232, 234. The third and fourth compliant capacitors236, 238 may include the same structural characteristics as the firstand second compliant capacitors 232, 234, but for their orientationrelative to the first and second compliant capacitors 232, 234.

As in the embodiments described above, the first and second compliantcapacitors 232, 234 may sense bending movement and provide data of afirst angular displacement 260 in a first plane 270, the angulardisplacement 260 being measured between the first and second vectors252, 254 defined by the first and second rigid members 216, 218.Likewise, the third and fourth compliant capacitors 236, 238 may sensebending movement of the angular displacement sensor 212 relative to asecond angular displacement 262 defined within a second plane 272, thefirst plane 270 being orthogonal to the second plane 272. Similarly, thesecond angular displacement 262 may be measured and calculated betweenthe first and second vectors 252′, 254′ defined by the first and secondrigid members 216, 218 relative to their orientation in the second plane272. The second plane 272 may be defined along the axis 224 of theangular displacement sensor 212 (co-axial with the first and secondvectors 252′, 254′) and orthogonally oriented relative to a widthdimension 244′ of the third and fourth compliant capacitors 236, 238.Similarly, the first plane 270 may be defined along the axis 224 of theangular displacement sensor 212 and orthogonally oriented relative to awidth dimension 244 of the first and second compliant capacitors 232,234. With the arrangement of the depicted embodiment, the sensor system210 may determine a first angular displacement relative to the firstplane 270 and a second angular displacement relative to the second plane272 via the corresponding respective first and second compliantcapacitors 232, 234 and the third and fourth compliant capacitors 236,238. The first, second, third and fourth compliant capacitors 232, 234,236, 238 extend within the elongated structure of the angulardisplacement sensor 212 as described herein.

The third and fourth compliant capacitors 236, 238 may be formedsimilarly to the first and second compliant capacitors 232, 234, as setforth herein. For example, the third and fourth compliant capacitors236, 238 may each include the outer and inner electrodes 38, 40 (notindividually illustrated in FIG. 9B as shown in FIG. 2B) with thenon-conductive dielectric layer 42 therebetween, as well as including aspring electrode 50 extending along or partially embedded in each of theouter and inner electrodes 38, 40 (see FIGS. 2A and 2B).

As depicted in FIG. 9C, the sensor system 210 of this embodiment may bepositioned along an anatomical joint 80, such as an ankle joint. Suchalso may be employed with other anatomical joints 80 in the anatomy,such as a shoulder joint and a hip joint, and even the knee and elbowjoints described herein. In another embodiment, the sensor system 210may be employed along the neck and back of a user.

With respect to FIG. 10A, another embodiment of a sensor system 310,only partially showing a sensor portion, is provided. In thisembodiment, the sensor system 310 may include an angular displacementsensor 312 including a single compliant capacitor (not shown) with ahelical orientation about the center axis 324 or a pair of compliantcapacitors 331 oriented in a cohelical fashion extending through theelongated structure 314 of the angular displacement sensor 312. Suchhelical compliant capacitors 331 may be in addition to, or instead of,first and/or second sets of compliant capacitors extending linearly andparallel through the elongated structure 314, as described above inother embodiments. Such helical compliant capacitors 331 may be sizedand configured to sense torque or twisting in the angular displacementsensor 312 and provide angular displacement 361 about the axis 324 ofthe angular displacement sensor 312 relative to the orientation of thefirst and second rigid members (not shown in FIG. 10A) moved between anon-rotated position to one or more rotated positions. This rotationalmotion defines an angular displacement within a third plane (not shown),which is orthogonal to the planes 270 and 272 (illustrated in FIG. 9A)and which measures the torsion (e.g., torsional displacement) about axis324. In such an arrangement, twisting in one direction induces apositive change in capacitance in one compliant capacitor and a negativechange of capacitance in a second compliant capacitor, the differentialmeasurement of which yields a value proportional to the angulardisplacement about the axis 324 within the third aforementioned plane.In the case of one single compliant capacitor, the positive change ornegative change in capacitance can be used to determine angulardisplacement about the axis 324. With this arrangement, the sensorsystem 310 may include the helical compliant capacitors 331 extendingwith a helical or cohelical configuration through the elongatedstructure 314 and along the longitudinal length of the elongatedstructure 314. Further, the sensor system 310 may also include the firstand second compliant capacitors 332, 334 and/or the third and fourthcompliant capacitors 336, 338, set forth in some embodiments describedabove, including the spring electrode 50 (FIGS. 2A and 2B) positionedalong each of the outer and inner electrodes of each compliantcapacitor, as described herein. Such spring electrode 50 may also beintegrated along each side of the helical compliant capacitors 331. Suchhelical compliant capacitors 331 may be formed with similar componentsas the first and second compliant capacitors 332, 334 such that eachhelical compliant capacitors 331 include the inner and outer electrodeswith the elastomer dielectric layer therebetween. By incorporatinghelical or cohelical compliant capacitors 331 along with compliantcapacitor pairs 332, 334 and 336, 338, angular displacement in threeorthogonal planes may be measured. The helical or cohelical compliantcapacitors 331 may be placed either on the outside of compliantcapacitor sets 332/334 and 336/338 or on the inside, or between thesecompliant capacitor sets. Advantageously, the sensor system 310 of thisembodiment may be employed over anatomical joints that may provide somerotation, such as, for example, the shoulder joint and the hip joint aswell as the neck and back and, further, anatomical joints that providebending movement in the first plane 270 and/or the second plane 272 (seeFIGS. 2B, 9A, and 9B), as described herein. It is noted that the angulardisplacement about axis 324 may be used in conjunction with the angulardisplacements 260 and 262 in order to perform a calibration of athree-axis sensor system 314 that will allow for the measurement of thethree aforementioned angular displacements that will be accurate overall possible deformations of the sensor system 310. In particular, theangular displacement about axis 324 can be used to compensate for errorsin the measurement of angular displacements 260 and 262 induced bytwisting of the sensor 314 about the axis 324. In this calibration, theraw output from the measurement of compliant capacitor pairs 331, 332,334 and 336, 338 may be used in conjunction with an appropriatecalibration procedure while the angular displacement sensor 312 is movedthrough its full range of motion throughout all three planes and curvefit to an appropriate multidimensional function.

In some embodiments, a calibration curve relates an output of theangular displacement sensor 312 in a single plane or multiple orthogonalplanes to conventional systems of angle measurement, such as degrees orradians, and compensates for errors in angular displacement measurementresulting in twisting of the elongated structure 314 and cross talk oftwo or more compliant capacitors in orthogonal planes, which may resultfrom imperfections in manufacturing measurement circuit design andconstruction.

For example, with respect to FIGS. 10B and 10C, the sensor system 310described relative to FIG. 10A may be positioned adjacent anatomicaljoints 80, such as shoulder or hip joints, respectively depicted. In oneembodiment, the first rigid member 316 may be positioned proximal theshoulder/hip joint and the second rigid member 318 may be positioneddistal the shoulder/hip joint such that the angular displacement sensor312 extends over and/or to the side of the shoulder/hip joint. With thesensor system 310 of this embodiment, the sensor system 310 may senserotational movement about axis 324, between the first and second rigidmembers 316, 318, as well as bending movement relative to an angulardisplacement 260, 262 in a first plane 270 and a second plane 272 (seeFIGS. 9A and 9B), as described herein. Further, the sensor system 310 ofthis embodiment may include all of the features and components discussedin the embodiments of the sensor system 10 described above, includingbeing coupled to the interface device 20 with its various components(including the biofeedback device 110, memory 122, and micro-controller114) for logging data 142 and transferring such data to a remote device22 for further analysis (see FIGS. 5A and 7). In this manner, the user84 may obtain useful data of the user's progress or decline of twistingand bending movement in the anatomical joints 80 of the user over one ormore sessions of employing the sensor system 310.

As will be apparent to one of ordinary skill in the art, the variousembodiments of the sensor system described herein may be employed withother portions of the human anatomy, such as, the various digits of thehuman anatomy as well as any other moving joint, appendage or portion ofthe human anatomy. Further, the sensor system may also be employed withrobotic arms, mechanical positioning devices, and rotary actuators, orany other suitable structure that may be useful to analyze or obtaininformation from not only in, for example, the medical and physicaltherapy industries, but also industries involving sports and athletics,computer and gaming systems, the entertainment industry involving,theater, animation, computer generation imaging and so forth.

Referring to FIG. 11, another embodiment of the sensor system 1100 forsensing angular displacement between two vectors 1152, 1154 defined byrigid members is provided. The sensor system 1100 may include similarcomponents as the sensor system 10 of FIG. 1A, the sensor system 210 ofFIG. 9, or the sensor system 310 of FIG. 10A. The sensor system 1100 mayinclude the angular displacement sensor 1112 (e.g., angular displacementsensor 12, angular displacement sensor 212, or angular displacementsensor 312), which may measure a single, two or three orthogonal angulardisplacement values, and one or more inertial measurement units (IMUs)1110, 1120. The IMUs 1110, 1120 may include any combination ofaccelerometers, gyroscopes, global positioning system (GPS) units, andthe like. As illustrated, the sensor system 1100 includes two IMUs 1110,1120. The one or more IMUs may be coupled to one or more rigid membersof the sensor system 1100. For example, the first IMU 1110 may becoupled to a first rigid member (e.g., first rigid member 16 of FIG. 1A)and the second IMU may be coupled to a second rigid member (e.g., secondrigid member 18 of FIG. 1A). The angular displacement sensor 1112 mayhave rigid ends defined by the coordinate systems X₁ and X₂ and maymeasure an angular displacement vector (AO), where this vector isdefined by three angular displacements in orthogonal planes. Each IMU1110, 1120 measures acceleration vectors (a₁ and a₂) and angularvelocity vectors (α₁ and α₂), respectively. In some embodiments, theaxis of each IMU 1110, 1120 may be aligned with the angular displacementsensor end vectors 1152, 1154, respectively. Alternatively, the axis ofeach IMU 1110, 1120 may be offset with the angular displacement sensorend vectors 1152, 1154, respectively.

FIG. 12 illustrates another embodiment of a sensor system 1200 thatincludes two instrumented registration members 1290 that are coupled toan angular displacement sensor 1212, in accordance with someembodiments. The sensor system 1200 may include similar components asthe sensor system 10 of FIG. 1A, the sensor system 210 of FIG. 9, or thesensor system 310 of FIG. 10A. For example, the angular displacementsensor 1212 may be similar to the angular displacement sensor 12,angular displacement sensor 212, or angular displacement sensor 312, asdescribed herein, and the registration members 1290 may be similar tothe registration members 90 described herein. The angular displacementsensor 1212 is coupled between the two instrumented registration members1290. The instrumented registration members 1290 are coupled to orotherwise include rotational sensors 1210 a-d to measure an angle α_(i)between an axis 1215 of a registration member 1290 and a vector 1220defined by a rotating member (not shown) that may rotate about axis1205. The rotational sensors 1210 a-d may also be angular sensors or acombination of rotational and angular sensors that measure the angleα_(i) between the axis 1215 and the vector 1220. As the rotating memberrotates about the axis 1205, the angle α_(i) between the axis 1215 andthe vector 1220 changes. Although four rotational sensors 1210 a-d areillustrated in the depicted embodiment, in other embodiments, one ormore such sensors may be used.

FIG. 13 illustrates the sensor system of FIG. 12 in greater detail,which includes one or more instrumented registration members 1290 thatmay be used to detect movement of a body part 1305, in accordance withsome embodiments. For the sake of illustration, the body part 1305 isdepicted as a leg with a knee joint. The registration members 1290 maynot align with an anatomical axis (dashed line) 1315 of the body part,which may result in an angle α_(i) and β_(i) between an axis 1320 of theregistration members 1290 and an axis 1330 of the rotational sensors1210 a-d. By taking the average of these values across each of therotational sensors 1210 a-d, the angular difference between the sensoraxis 1330 and anatomical axis 1315 can be measured at both ends of thesensor system 1200. As illustrated, the sensor system 1200 includes fourrotational sensors 1210 a-d, with one rotational sensor attached on eachend of two registration members 1290, though any number of rotationalsensors 1210 may be used.

Now with reference to FIG. 14, a sensor system 1400 is depicted in usewith an angular displacement sensor 1412 extending over an anatomicaljoint 80, such as a knee joint, with the first and second rigid members1416, 1418 coupled to a leg 82 of a person, similar to the leg 82 asillustrated in FIG. 5A. The sensor system 1400 may include similarcomponents as the sensor system 10 of FIG. 1A, the sensor system 210 ofFIG. 9, or the sensor system 310 of FIG. 10A. The sensor system 1400 canalso include one or more registration members 1490. In one embodiment,sensor system 1400 includes a rigid but flexible support 1410 (e.g., awire support), which prevents the sensor system 1400 from sliding downthe leg 82. The default position of the sensor 1412 may include a bendto facilitate a more comfortable brace. Support of this structure forthe sensor 1412 may be facilitated by the support 1410.

In some embodiments, the first rigid member 1416 is configured to beremovably fixed and positioned proximal the anatomical joint 80 and thesecond rigid member 1418 is configured to be removeably fixed andpositioned distal the anatomical joint 80 such that the angulardisplacement sensor 1412 extends adjacently over the anatomical joint 80to measure angular displacement of the anatomical joint 80.

FIG. 15 illustrates a motion sensing system 1500 with a removableangular displacement sensor 1512, in accordance with some embodiments.The motion sensing system 1500 may include similar components as thesensor system 10 of FIG. 1A, the sensor system 210 of FIG. 9, or thesensor system 310 of FIG. 10A. The motion sensing system 1500 mayinclude one or more registration members 1590 and a pocket 1510 thatreceives a removable angular displacement sensor 1512. The removableangular displacement sensor 1512 may be similar to any of the angulardisplacement sensors described herein, such as angular displacementsensor 12, angular displacement sensor 212, and angular displacementsensor 312, which measures one, two or three orthogonal angulardisplacements. The motion sensing system 1500 may also include on ormore IMU's as described herein. The removable angular displacementsensor 1512 may be slidably inserted into and removed from the pocket1510. In some embodiments, the removable angular displacement sensor1512 attaches to the motion sensing system 1500 via buttons, all-purposestraps (e.g., Velcro® straps) or by other means, such that the removableangular displacement sensor 1512 can be placed in different braces,garments or devices.

FIG. 16 illustrates a linked motion measurement system 1600, inaccordance with some embodiments. The linked motion measurement 1600 mayinclude similar components as the sensor system 10 of FIG. 1A, thesensor system 210 of FIG. 9, or the sensor system 310 of FIG. 10A. Inaddition, the linked motion measurement system 1600 may include multiplesensor systems 1610 located at different parts of a body. Asillustrated, the linked motion measurement system 1600 includes foursensor systems 1610 a-d. Each of the sensor systems 1610 may be linkedtogether either wirelessly or via data cables to form a single motionmeasurement system. Alternatively, each of the sensor systems 1610 maybe linked to a separate motion measurement system. Such data may be usedto perform any type of data analysis for movements of the body. Exampleanalysis can include inverse dynamics calculations to reconstruct muscleand joint forces and torques or for motion recognition.

In some embodiments, linked motion measurement system 1600 includessensing systems that are not attached to a body. For example, the linkedmotion measurement system 1600 may include one or more cameras that maybe used in conjunction with one or more of the sensor systems 1610 todetect motion. The linked motion measurement system 1600 may include acontroller coupled to the one or more cameras. The controller may usethe camera to detect the body and any movements of the body, asdescribed herein.

A method of measuring movement of an anatomical joint of a user using asensor system is also described. The sensor system may include similarcomponents as the sensor system 10 of FIG. 1A, the sensor system 210 ofFIG. 9, or the sensor system 310 of FIG. 10A. The sensor system mayinclude an angular displacement sensor (e.g., angular displacementsensor 12, angular displacement sensor 212, or angular displacementsensor 312), as described herein.

The method includes providing an angular displacement sensor having anelongated flexible structure defining an axis extending along alongitudinal length of the elongated structure between a first end and asecond end. The first end may be coupled to a first rigid member and thesecond end may be coupled to a second rigid member. The first rigidmember may define a first vector and the second rigid member may definea second vector. The first and second vectors may extend substantiallyco-axial with the axis of the elongated structure when the elongatedstructure is in a substantially linear non-bent position.

The method can also include positioning the first rigid member to theuser at a proximal position of the anatomical joint. The method canfurther include positioning the second rigid member to the user at adistal position of the anatomical joint. The elongated structure of theangular displacement sensor may adjacently extend over the anatomicaljoint of the user with the first and second rigid members positioned tothe user in a substantially fixed manner.

The method can also include measuring an angular displacement in one ormore orthogonal planes that is defined between the first and secondvectors when the elongated structure is moved from the substantiallylinear non-bent position to a bent position via a movement of theanatomical joint by the user. In some embodiments, measuring the angulardisplacement in one or more orthogonal planes includes measuring with adifferential measuring circuit associated with the angular displacementsensor. The angular displacement sensor may include at least onecompliant strain sensor having a width extending along the longitudinallength of the elongated structure, as described herein. In furtherembodiments, measuring the angular displacement in one or moreorthogonal planes includes measuring a change in the angulardisplacement in one or more planes between the first and second vectorsdefined by the respective first and second rigid members. In someembodiment, the method may also include generating biofeedback signalsto a user based on the measured angular displacement meeting inputparameters with at least one of an audible notification, a visualnotification, and a vibrational tactile notification.

The method may also include performing a calibration of the angulardisplacement sensor that accounts for misalignment between the first andsecond rigid members and the anatomical axis of the anatomical jointbeing measured.

In some embodiments, the method includes storing data in an interfacedevice coupled to the angular displacement sensor. The method may alsoinclude transferring the data to a remote device.

FIG. 17 illustrates a diagrammatic representation of a machine in theexample form of a computer system 1700 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies discussed herein, may be executed. The computer system1700 may correspond to the interface device 20 of FIGS. 1A, 5A and 7,remote device 22 of FIGS. 1A, 5A and 7, personal computer 102 of FIG.5A, micro-controller 114 that executes the control and analysis software124. The computer system 1700 may correspond to an IMU or a computersystem in communication with an IMU, as described herein. In embodimentsof the present invention, the machine may be connected (e.g., networked)to other machines in a Local Area Network (LAN), an intranet, anextranet, or the Internet. The machine may operate in the capacity of aserver or a client machine in a client-server network environment, or asa peer machine in a peer-to-peer (or distributed) network environment.The machine may be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, switch or bridge, or any machinecapable of executing a set of instructions (sequential or otherwise)that specify actions to be taken by that machine. Further, while only asingle machine is illustrated, the term “machine” shall also be taken toinclude any collection of machines (e.g., computers) that individuallyor jointly execute a set (or multiple sets) of instructions to performany one or more of the methodologies discussed herein.

The example computer system 1700 includes a processing device 1702, amain memory 1704 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) such as synchronous DRAM (SDRAM), a staticmemory 1706 (e.g., flash memory, static random access memory (SRAM),etc.), and a secondary memory 1716 (e.g., a data storage device), whichcommunicate with each other via a bus 1708.

The processing device 1702 represents one or more general-purposeprocessors such as a microprocessor, central processing unit, or thelike. The term “processing device” is used herein to refer to anycombination of one or more integrated circuits and/or packages thatinclude one or more processors (e.g., one or more processor cores).Therefore, the term processing device encompasses a microcontroller, asingle core CPU, a multi-core CPU and a massively multi-core system thatincludes many interconnected integrated circuits, each of which mayinclude multiple processor cores. The processing device 1702 maytherefore include multiple processors. The processing device 1702 mayinclude a complex instruction set computing (CISC) microprocessor,reduced instruction set computing (RISC) microprocessor, very longinstruction word (VLIW) microprocessor, processor implementing otherinstruction sets, or processors implementing a combination ofinstruction sets. The processing device 1702 may also be one or morespecial-purpose processing devices such as an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), adigital signal processor (DSP), network processor, or the like.

The computer system 1700 may further include one or more networkinterface devices 1722 (e.g., NICs). The computer system 1700 also mayinclude a video display unit 1710 (e.g., a liquid crystal display (LCD)or a cathode ray tube (CRT)), an alphanumeric input device 1712 (e.g., akeyboard), a cursor control device 1714 (e.g., a mouse), and a signalgeneration device 1720 (e.g., a speaker).

The secondary memory 1716 may include a machine-readable storage medium(or more specifically a computer-readable storage medium) 1724 on whichis stored one or more sets of instructions 1754 embodying any one ormore of the methodologies or functions described herein. Theinstructions 1754 may also reside, completely or at least partially,within the main memory 1704 and/or within the processing device 1702during execution thereof by the computer system 1700; the main memory1704 and the processing device 1702 also constituting machine-readablestorage media.

While the computer-readable storage medium 1724 is shown in an exampleembodiment to be a single medium, the term “computer-readable storagemedium” should be taken to include a single medium or multiple media(e.g., a centralized or distributed database, and/or associated cachesand servers) that store the one or more sets of instructions. The term“computer-readable storage medium” shall also be taken to include anymedium other than a carrier wave that is capable of storing or encodinga set of instructions for execution by the machine that cause themachine to perform any one or more of the methodologies of the presentembodiments. The term “computer-readable storage medium” shallaccordingly be taken to include, but not be limited to, non-transitorymedia such as solid-state memories, and optical and magnetic media.

The modules, components and other features described herein can beimplemented as discrete hardware components or integrated in thefunctionality of hardware components such as ASICS, FPGAs, DSPs orsimilar devices. In addition, the modules can be implemented as firmwareor functional circuitry within hardware devices. Further, the modulescan be implemented in any combination of hardware devices and softwarecomponents, or only in software.

Some portions of the detailed descriptions which follow are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, as apparent from the followingdiscussion, it is appreciated that throughout the description,discussions utilizing terms such as “identifying”, “probing”,“establishing”, “detecting”, “modifying”, or the like, refer to theaction and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within the computer system's registersand memories into other data similarly represented as physicalquantities within the computer system memories or registers or othersuch information storage, transmission or display devices.

Embodiments of the present invention also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, or it may comprise a generalpurpose computer system selectively programmed by a computer programstored in the computer system. Such a computer program may be stored ina computer readable storage medium, such as, but not limited to, anytype of disk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic disk storage media, opticalstorage media, flash memory devices, other type of machine-accessiblestorage media, or any type of media suitable for storing electronicinstructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear as set forth in thedescription above. In addition, the present embodiments are notdescribed with reference to any particular programming language. It willbe appreciated that a variety of programming languages may be used toimplement the teachings of the embodiments as described herein.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. Although the present embodiments has been describedwith reference to specific examples, it will be recognized that theinvention is not limited to the embodiments described, but can bepracticed with modification and alteration within the spirit and scopeof the appended claims. Accordingly, the specification and drawings areto be regarded in an illustrative sense rather than a restrictive sense.The scope of the invention should, therefore, be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. An apparatus comprising: an elongated structure extending between a first end and a second end, the elongated structure being compliant material that is flexible and bendable from a linear, non-bent position to multiple bendable positions; and a first compliant capacitor oriented in a helical fashion along an axis of the elongated structure when the elongated structure is in the linear, non-bent position, wherein the first compliant capacitor comprises a first conductive layer embedded within and extending from the first end to the second end along a longitudinal length of the elongated structure to form a first electrode of the first compliant capacitor, a second conductive layer embedded within and extending from the first end to the second end along the longitudinal length to form a second electrode of the first compliant capacitor, and a first elastomer dielectric layer extending between the first conductive layer and the second conductive layer, wherein a first capacitance of the first compliant capacitor is measured to sense a torsional displacement of the elongated structure.
 2. The apparatus of claim 1, wherein the apparatus further comprises a plurality of compliant capacitors having a width and extending along the longitudinal length of the elongated structure.
 3. The apparatus of claim 1, further comprising: a second compliant capacitor, wherein the second compliant capacitor comprises a third conductive layer embedded within and extending from the first end to the second end along the longitudinal length of the elongated structure to form a third electrode of the second compliant capacitor, a fourth conductive layer embedded within and extending from the first end to the second end along the longitudinal length to form a fourth electrode of the second compliant capacitor, and a second elastomer dielectric layer extending between the third conductive layer and the fourth conductive layer, wherein a second capacitance of the second compliant capacitor is measured to sense an angular displacement of the elongated structure.
 4. The apparatus of claim 3, further comprising: a first member coupled to the first end of the elongated structure, the first member defining a first vector corresponding with the axis of the elongated structure; and a second member coupled to the second end of the elongated structure, the second member defining a second vector corresponding with the axis of the elongated structure, and wherein an angular displacement is determined around the axis of the elongated structure when the angular displacement is applied to the first and second members.
 5. The apparatus of claim 4, wherein the first member is a first rigid member and the second member is a second rigid member.
 6. The apparatus of claim 3, further comprising a circuit coupled to the first compliant capacitor and the second compliant capacitor, the circuit to measure the first capacitance of the first compliant capacitor and the second capacitance of the second compliant capacitor, and to determine the torsional displacement around the axis based on the first capacitance and the angular displacement based on the second capacitance.
 7. The apparatus of claim 1, further comprising a first pair of compliant capacitors, wherein the first pair of compliant capacitors comprises a third conductive layer embedded within and extending from the first end to the second end along the longitudinal length of the elongated structure to form an outer electrode, a fourth conductive layer embedded within and extending from the first end to the second end along the longitudinal length to form an inner electrode, and a second elastomer dielectric layer extending between the third conductive layer and the fourth conductive layer, wherein the first pair of compliant capacitors are offset from the axis of the elongated structure and are reflected about the axis, wherein the axis is a center axis, and wherein bending movement of the elongated structure induces an opposing response between the first pair of compliant capacitors that is proportional to an applied strain on the elongated structure.
 8. The apparatus of claim 7, further comprising a second pair of compliant capacitors orientated orthogonal to the first pair of compliant capacitors and extending from the first end to the second end along the longitudinal length of the elongated structure, wherein the second pair of compliant capacitors are offset from the center axis of the elongated structure and are reflected about the center axis, and wherein bending movement of the elongated structure induces an opposing response between the second pair of compliant capacitors that is proportional to the applied strain on the elongated structure.
 9. The apparatus of claim 1, further comprising a third compliant capacitor oriented in a cohelical fashion along the axis of the elongated structure when the elongated structure is in the linear, non-bent position, wherein the third compliant capacitor comprises a fifth conductive layer embedded within and extending from the first end to the second end along the longitudinal length of the elongated structure to form a fifth electrode of the third compliant capacitor, a sixth conductive layer embedded within and extending from the first end to the second end along the longitudinal length to form a sixth electrode of the third compliant capacitor, and a third elastomer dielectric layer extending between the fifth conductive layer and the sixth conductive layer, wherein a third capacitance of the third compliant capacitor is measured to sense the torsional displacement of the elongated structure.
 10. The apparatus of claim 1, wherein the compliant material is an elastomer based material, wherein the capacitance of the first compliant capacitor changes in proportion to an applied torsional strain on the elongated structure, wherein the first electrode is a first conductive filler embedded within the elastomer based material, wherein the second electrode is a second conductive filler embedded within the elastomer based material, wherein the first conductive layer and second conductive layer extend in separate planes that are rotational about the axis throughout the elongated structure from the first end to the second end.
 11. The apparatus of claim 1, wherein the first electrode is formed as an elastomer matrix of a conductive filler embedded in the compliant material, and wherein the compliant material is an elastomer composite.
 12. An apparatus comprising: an elongated structure extending between a first end and a second end, the elongated structure being compliant material that is flexible and bendable from a linear, non-bent position to multiple bendable positions and is an elastomer based material; and a compliant capacitor comprising: a first conductive filler embedded within and extending from the first end to the second end along a longitudinal length of the elongated structure to form a first electrode of the compliant capacitor; a second conductive filler embedded within and extending from the first end to the second end along the longitudinal length to form a second electrode of the compliant capacitor, wherein the first conductive filler and the second conductive filler extend linearly in separate planes that are parallel relative to one another throughout the elongated structure from the first end to the second end; and an elastomer dielectric layer extending between the first conductive filler and the second conductive filler, and wherein a capacitance of the compliant capacitor changes in proportion to an applied strain on the elongated structure.
 13. The apparatus of claim 12, wherein the elastomer dielectric layer comprises at least one of a thermoset elastomer or a thermoplastic elastomer.
 14. The apparatus of claim 12, wherein the first conductive filler comprises a powdered conductor.
 15. The apparatus of claim 14, wherein the powdered conductor comprises nano particles.
 16. The apparatus of claim 12, wherein the compliant capacitor further comprises a spring electrode extending along, through or partially through the first electrode of the compliant capacitor, wherein the spring electrode is at least one of wavy or substantially flat.
 17. A sensor system comprising: an angular displacement sensor comprising: an elongated structure extending between a first end and a second end, the elongated structure being compliant material that is flexible and bendable from a linear, non-bent position to multiple bendable positions and is an elastomer based material; and a first compliant capacitor comprising: a first conductive filler embedded within and extending from the first end to the second end along a longitudinal length of the elongated structure to form a first electrode of the first compliant capacitor; a second conductive filler embedded within and extending from the first end to the second end along the longitudinal length to form a second electrode of the first compliant capacitor, wherein the first conductive filler and the second conductive filler extend linearly in separate planes that are parallel relative to one another throughout the elongated structure from the first end to the second end; and an elastomer dielectric layer extending between the first conductive filler and the second conductive filler, wherein the first end defines a first vector corresponding with an axis of the angular displacement sensor when the elongated structure is in the linear, non-bent position, wherein the second end defines a second vector corresponding with the axis of the angular displacement sensor, and wherein an angular displacement is determined between the first vector and the second vector within a first plane defined and extending along the longitudinal length and extending orthogonal through a width of the first compliant capacitor.
 18. The sensor system of claim 17, further comprising: a first member coupled to the first end of the angular displacement sensor; and a second member coupled to the second end of the angular displacement sensor.
 19. The sensor system of claim 17, further comprising a circuit coupled to the first compliant capacitor, the circuit to measure a capacitance of the first compliant capacitor to sense bending movement of the elongated structure, and wherein the circuit is configured to determine the angular displacement between the first and the second vector based on the measured capacitance.
 20. The sensor system of claim 17, wherein the angular displacement sensor comprises a plurality of compliant capacitors having a width and extending along the longitudinal length of the elongated structure and spaced from the first compliant capacitor in a parallel manner such that a sensitivity of the angular displacement is increased. 